Although clinical studies using guarana are not available, anecdotal evidence has suggested that it may produce similar effects to caffeine on subjective feelings of wellbeing, energy, motivation and self-confidence. Guarana may exert a mild antidepressant effect as demonstrated in forced-swimming and open field tests in mice
ENHANCED COGNITIVE FUNCTION AND ALERTNESS
Two recent double-blind studies have confirmed that guarana has significant effects on cognitive function and provide evidence that these effects are not just mediated by the herb’s caffeine content.
One double-blind, placebo-controlled study assessed the effects of four different doses of guarana (37.5, 75, 150 and 300 mg) in 22 subjects. Cognitive performance and mood were assessed at baseline and again 1, 3 and 6 hours after each dose using the Cognitive Drug Research computerised assessment battery, serial subtraction tasks, a sentence verification task and visual analogue mood scales. All doses improved picture and word recognition, results on the Bond-Lader visual analogue scales and caffeine research visual analogue scales showing improvements in alertness and reduced ratings of headache. The two lower doses produced better results than the two higher doses, which were associated with impaired accuracy of choice reaction and on one of the subtraction tests. Several observations suggest that these effects were not due to caffeine alone. Firstly, effects were still apparent 6 hours after administration and secondly, better results were obtained with a dose of 37.5 mg than 300 mg with a caffeine content of less than 5 mg in the lowest dose.
Another double-blind, placebo controlled study investigated the effects of a single dose of guarana (75 mg) on cognition, in combination with and in comparison to ginseng (Panax ginseng 200 mg) in 28 healthy volunteers. Guarana was shown to produce comparable effects to ginseng in improved task performance with all three treatments better than placebo. However, guarana was superior to ginseng in improving the speed of performed tasks. Once again, given the low caffeine content (9 mg) of the guarana extract used in that study, the effects are unlikely to be attributable to its caffeine content alone, particularly as the dose was shown to be as effective as a 16-fold dose of pure caffeine.
Two previous randomised, double-blind studies have investigated the effects of guarana on cognitive function and produced negative results. One study involving 45 healthy elderly volunteers found that guarana treatment was ineffective, which confirmed the findings of a previous study conducted by the same authors. Studies in some animal models have produced positive results for both single-dose and long-term administration of guarana, observing a positive effect on memory acquisition and memory maintenance.
Guarana is also used as an ergogenic aid by some athletes, most likely because caffeine and theophylline have been used in this way, to improve performance in training and competition. No human studies testing guarana for effects on physical performance could be located. Referring to caffeine studies, it appears that ergogenic effects are observed under some conditions but not others. Testing guarana in several animal models has also produced contradictory results. Significant increases in physical capacity have been observed with a dose of 0.3 mg/mL of a guarana suspension after 100 and 200 days’ treatment. However, the same effect was not seen with a concentration of 3.0 mg/mL nor of a solution of caffeine 0.1 mg/mL.
APPETITE SUPPRESSANT AND WEIGHT-LOSS AID
Weight-loss products often contain guarana, in the belief that it suppresses appetite and may have thermogenic and diuretic activities. An animal study designed to evaluate the effects of guarana and decaffeinated guarana found that only the caffeinated herb was effective for weight loss. To date, most clinical studies have investigated the effects of guarana in combination with other herbs. A double-blind, RCT testing a combination of yerbe mate (leaves of Ilex paraguayenis), guarana (seeds of Paullinia cupana) and damiana (leaves of Turnera diffusa var. aphrodisiaca) found that the preparation significantly delayed gastric emptying, reduced the time to perceived gastric fullness and induced significant weight loss over 45 days in overweight patients. Another randomised double-blind placebo-controlled trial evaluated the effects of guarana in combination with Ma Huang (Ephedra spp.) and concluded that the formula was effective for weight-loss in overweight men after 8 weeks of treatment. Although encouraging, the effects of guarana as a stand-alone treatment need to be confirmed.
ACCORDING TO CLINICAL TRIALS
• Cognition, alertness and mood: doses between 37.5 and 75 mg are sufficient to provide effects for at least 6 hours.
For other indications, guarana has not been significantly researched. Based on caffeine content, it is advised that doses should not exceed that amount that will provide approximately 250 mg of caffeine daily. This is equivalent to 2.5-4 g guarana/day, depending on the caffeine content of the preparation.